Crystal structure analysis of epitaxial BiFeO₃-BiCoO₃ solid solution films grown by metalorganic chemical vapor deposition

Epitaxial (001)-oriented (1 - x)BiFeO₃-xBiCoO₃ solid solution films with x = 0-0.33 were grown on (100)SrTiO₃ substrates at 700°C by metalorganic chemical vapor deposition. The crystal structure of the films was characterized by high-resolution X-ray diffraction analysis and Raman spectroscopy. Unit cell volume and the lattice parameter were changed with increasing x. The BiFeO₃ film with = 0 has rhombohedral symmetry and those with x = 0.16 and 0.21 have a mixture of rhombohedral and tetragonal symmetries. Finally, tetragonal symmetry was observed for the film with x = 0.33 together with a small amount of the contamination phase. This result suggests that the symmetry of (1 - x)BiFeO₃-xBiCoO₃ films changed from rhombohedral to tetragonal with increasing x similarly to Pb(Zr,Ti)O ₃ having a large piezo response.